Herman Cain's "9-9-9" tax reform proposal deserves serious consideration — as does the "15-15-15" proposal that I have previously outlined. I'd eliminate the personal income, corporate income, and estate and gift taxes and replace them with a highly progressive payroll tax, a highly progressive retail sales tax, and a highly progressive inheritance tax. Under my plan, households and firms would not need to file annual tax returns. Under Mr. Cain's, they would. My plan is also significantly more progressive and would raise more revenue.

The current system is broken. In trying to fix it, Herman Cain gets a lot right.

Cain’s plan would eliminate the 15.3 percent payroll tax, which we economists believe falls disproportionately on workers and is highly regressive, hitting the poor on every dollar they earn and exempting the rich on virtually all of their earnings.

Cutting the corporate income tax is also, arguably, progressive. Many economists believe the corporate income tax is borne primarily by workers because when the tax is high, corporations gradually move operations to other countries, leaving workers with fewer jobs at lower pay. I score Cain’s corporate tax rate as a plus for the poor.

Cain’s proposal for a 9 percent retail sales tax would target consumption, affecting both the rich and the poor. But Cain would not tax the “imputed rental services” that we enjoy from existing owner-occupied homes, planes, boats and cars, which the rich own disproportionately. There is also no mention of a demogrant — a monthly payment based only on household size that’s large enough to ensure the poor pay no sales taxes on net. (FairTaxers call this a prebate.) Nor would Cain tax consumption done abroad. The Purple Tax suffers from none of these shortcomings.

Under today’s system, people in the lowest tax bracket pay no income tax at all. Cain’s 9 percent income tax would hit the poor on the first dollar earned. In addition, the poor would, if I have it right, lose the Earned Income Tax Credit, which is our largest poverty-relief program. And exempting capital gains from the 9 percent tax is silly. There is no economic basis for taxing one return to capital differently from another.

On balance, Cain’s “9-9-9” plan appears more regressive than the current system and seems to shift more of the tax burden from the old onto the young, because it so greatly reduces taxes on income from sources like dividends.

But figuring this out requires real study. A New York Times editorial vehemently denounced Cain’s plan as highly regressive. I don’t think anyone has done the careful work needed to say this. The more sound conclusion at this stage would be that it’s a plan worth studying, and if it proves regressive — as measured by economists, not Congress — it could be modified.